Understanding Map Projections

GEOGRAPHIC COORDINATE SYSTEM
Geographic coordinates displayed as if the longitude–latitude
values are linear units. An equivalent projection is
Equirectangular with the standard parallel set to the equator.
DESCRIPTION
The geographic coordinate system is not a map
projection. The earth is modeled as a sphere or
spheroid. The sphere is divided into equal parts
usually called degrees; some countries use grads. A
circle is 360 degrees or 400 grads. Each degree is
subdivided into 60 minutes, with each minute
composed of 60 seconds.
The geographic coordinate system consists of
latitude and longitude lines. Each line of longitude
runs north–south and measures the number of
degrees east or west of the prime meridian. Values
range from -180 to +180 degrees. Lines of latitude
run east–west and measure the number of degrees
north or south of the equator. Values range from +90
degrees at the North Pole to -90 degrees at the South
Pole.
The standard origin is where the Greenwich prime
meridian meets the equator. All points north of the
equator or east of the prime meridian are positive.
USES AND APPLICATIONS
Map projections use latitude and longitude values to
reference parameters such as the central meridian,
the standard parallels, and the latitude of origin.
Supported map projections• 59